This invention relates to optical communications, and more particularly to a method and apparatus for tracking alignment in optical communications systems.
Optically-based wireless transceiver systems have provided revolutionary advancements in the field of communications. Such systems have become increasingly prevalent and have been implemented for many practical applications. For example, optical communications are used for data gathering functions such as video-conferencing, E-mail, fax, television, digital radio communications, and a variety of networking applications. The popularity of optical systems can be attributed to their numerous beneficial characteristics. Optical systems are wireless; thus, physical installation is relatively simple. Noise and interference problems associated with other types of wireless communications have largely been eliminated with the advent of optical systems. The total power consumption for most optical systems is comparably low. These and other benefits have made wireless optics an increasingly popular communication technique.
One shortcoming of existing wireless optical systems is the requirement that the transmitting source be properly aligned with the receiving source. Without proper alignment, the optical receiver cannot effectively evaluate the optical beam to perform data recovery. The problem is exacerbated where substantial electrical noise in the environment interferes with the optical receiver. Such interference may falsely trigger the system to recognize an optical beam when none was in fact transmitted. In contrast, systems using hardware connections, such as fiber optics systems, do not require transmitter-receiver alignment. The transmitted wave simply follows the contour of the wire or other transmission media until it reaches the receiver.
Nevertheless, a wireless optical receiving system having a very efficient correction mechanism would minimize alignment problems while preserving the remaining substantial benefits associated with wireless optical communications.
Also, for maximum efficiency, it is desirable to implement an optical system which can effectively process a low-energy optical beam. Having such a system, low power optical signals can be transmitted and decoded at the receiving end such that a minimum amount of energy is expended in the process.
To perform these tasks, an optical communication system must be capable of automatically realigning the transmitter and receiver which, for whatever reason, have become misaligned. Unfortunately, current technology requires that multiple receiving elements be used for receiver realignment and data gathering. The use of multiple elements, among other things, increases cost and power consumption while decreasing overall system efficiency.
As an illustration, one prior art optical receiving communication system uses a separate quadrant sensor, positioned in the line-of-sight of the optical transmitter, to detect and correct alignment errors. The system also uses a collecting lens to project the received beam onto a photodiode for data recovery. Disadvantageously, this approach requires at least three distinct elements (a quadrant sensor, a collecting lens, and a photodiode) to implement the system's optical receiver. Thus, multiple optical receiving elements are required to implement data recovery and directional accuracy tracking, which complicates and increases the cost of the receiving system. Another disadvantage of this system is its inefficient use of transmitted optical power. In particular, after evaluating the alignment accuracy of the transmitted beam, the quad sensor must then permit photons of the beam to pass through the sensor to a second apparatus (collecting lens and photodiode) for data recovery. The transmitted beam must contain sufficient signal power to enable the beam to pass enough photons to the photodiode through a small aperture in the quad sensor. This prior art configuration places practical limits on the minimum achievable transmitted signal power. While further drawbacks to this prior art approach are omitted from discussion, they will be apparent to practitioners in the art.
It is therefore an object of the invention to provide a more simplified, compact and robust method and apparatus for processing received optical signals.
It is still another object of the invention to provide a method and apparatus for using a single optical receiving element to perform both data recovery functions and tracking accuracy evaluations.
It is further an object of the invention to provide a more efficient optical communication system which requires less power consumption than existing systems.